The invention relates to the configuration of the use of compression in packet-switched data transmission.
Third-generation mobile systems, called at least UMTS (Universal Mobile Telecommunication System) and IMT-2000 (International Mobile Telephone System), will provide not only circuit-switched, typically speech services, but also packet-switched services for instance in the manner of the packet radio network GPRS (General Packet Radio Service) designed for the GSM system. Packet-switched data transmission enables the use of different data services by means of a mobile station and, on the other hand, the allocation of the resources of a mobile system, especially the radio interface, to each user as is necessary.
When a packet-switched connection is used, the radio resource management RRM system of the UMTS system allocates parameters to a radio bearer, the parameters specifying the properties of the radio bearer used. One of the parameters specifying a radio bearer is the method of compressing the header fields of the data packets used by the terminal. In the UMTS system, header fields are compressed in data packets to be transmitted and decompressed in data packets to be received on a packet data convergence protocol layer PDCP belonging to the packet data protocol. Several header field compression methods supported by a terminal are typically configured for it. In the present development versions of the UMTS system, the header field compression method to be used on a radio bearer is configured in such a way that before a connection is set up, the terminal informs the radio access network RAN of the compression methods supported by the terminal. The RAN uses this information to decide whether header field compression is to be used on the packet-switched connections of said terminal, and which compression method is used.
The problem in the above arrangement is that the user of a terminal has no effect on whether or not header field compression is used on packet-switched connections. Header field compression is often preferable, since it allows the limited radio resources to be used more efficiently to transfer payload. However, situations and applications exist wherein header field compression is not preferable, such as when the limited processing capacity of a terminal is to be saved or if the compatibility of applications requires this on a radio bearer. In the UMTS system, the user of a terminal cannot configure header field compression so as to be suitable for each particular situation, but, instead, the configurations set by the RAN are used on all data links, i.e. PDP contexts (Packet Data Protocol Context) of the terminal.
A method of configuring compression methods for header fields (PCOMP, Protocol control information Compression, also known as HCOMP, Header Compression) and user data (DCOMP, Data Compression) is known from the GSM-based GPRS system, wherein a header field and user data compression method is negotiated for each PDP context upon activation of the PDP context by means of a context identifier CID field. This allows the user of the terminal to influence the compression parameters to be used and whether compression is to be used at all. However, such a negotiation mechanism does not exist in the UMTS system. This is why a suitable way to offer the user of a terminal a chance to influence the configuration of compression methods has to be found for the UMTS system.